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396 vs 454 bigblock engines

J

jrcpi999

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Thornton, CO
77 blazer 4x4. I have a built 350 getting 8 MPG with no power. Something is wrong. When I got the truck, the guy had put 2 different heads on so I assume something is wrong and explains no power. I have a friend giving me the option of a 396 BB or 454 BB stock engines to build. I am leaning toward the 396 but just wanted to see if anyone has any opinions as to which would be a better engine?
 
jrcpi999 said:
77 blazer 4x4. I have a built 350 getting 8 MPG with no power. Something is wrong. When I got the truck, the guy had put 2 different heads on so I assume something is wrong and explains no power. I have a friend giving me the option of a 396 BB or 454 BB stock engines to build. I am leaning toward the 396 but just wanted to see if anyone has any opinions as to which would be a better engine?
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you're running those 3.07 gears, you're not going to feel any "power" the truck is lugging to get moving.

go with some 4.56's or 4.88's and it will wake up, of course you lose some of your highway mileage though...
 
Don't waste your time with the 396.

It's the "baby" of the big block family....better suited to a musclecar than a heavy truck. Seriously, the costs to rebuild a 396 vs. 454 will be about the same so you might as well get the extra cubes (aka. POWER).

Build the motor for "bottom end" torque when you do it. There isn't much point building for peak HP numbers unless you are doing mudbog type 4-wheeling.


:usaflag:
 
Cool. I was planning on building for bottom end and I know the cost would be the same. This will go in after I redo the axles no doubt. I was just heard that the 396 would get a little better gas mileage. Thats why I was leaning toward that.
 
You want mileage drop in a diesel...you want a BBC poor mileage should be a foregone conclusion.

Rene
 
jrcpi999 said:
Cool. I was planning on building for bottom end and I know the cost would be the same. This will go in after I redo the axles no doubt. I was just heard that the 396 would get a little better gas mileage. Thats why I was leaning toward that.
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Go for the 454. And if the cranks shot, make it a 496.

My Blazer gets 9mpg now matter what I'm doing. Idling around town, 65 down the highway, pulling a loaded car trailer. That's with a built 350, 465/205, 4.88's, and 36" tires. I don't expect the 454 I'm building to be any better.
 
HAHAHAHAHAHAHAHAAAAAAA

You're going to be drinking fuel with a BBC either way. Remember though if you build the motor to be powerful at the RPM where it will spend most of it's time running, you give yourself the best chance at economy.

Big blocks tend to make plenty of power at low RPMS (2000 - 2200RPM) so if you are running in OD on the highway (or have 3.08 gears) odds are good that it won't take much throttle to keep the truck moving. A 350 small block would be working a lot harder to make the same power (more throttle required).... you MIGHT not lose much in the way of MPGs vs.a smallblock, but the #1 thing you can do to improve mileage is drive as slowly as you can stand it on the highway.

Pushing the K5 brick down the highway at 75MPH takes a LOT more power/fuel than only running at 55MPH.....


:usaflag:
 
HAHAHAHA!!! This is hilarious and also very poor in my truck. With the built 350 I have(power in the low RPM build), TH350, and those awful 3.07 gears, I am averagin 5.63MPG now. I would be HAPPY to get to 9MPG!!!!!!
 
Man i've had a motor bout ready to blow, 3.07 gears, and a 350 turbo and i STILL managed to get 8mpg :doah:
 
Randy92782 said:
Man i've had a motor bout ready to blow, 3.07 gears, and a 350 turbo and i STILL managed to get 8mpg :doah:
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TELL ME ABOUT IT!!! I dont think this guy knew what he was doing when he rebuilt the motor. I do know that he has 2 different heads on it and the valves were measured by a shop when I had the heads off and they are too small o be chevy. He also had 3 different size valves. Thats why I am looking into the bigger engine. Plus not to mention that it will be free with some new parts. Buddy owes me money for working on his jeep
 
jrcpi999 said:
TELL ME ABOUT IT!!! I dont think this guy knew what he was doing when he rebuilt the motor. I do know that he has 2 different heads on it and the valves were measured by a shop when I had the heads off and they are too small o be chevy. He also had 3 different size valves. Thats why I am looking into the bigger engine. Plus not to mention that it will be free with some new parts. Buddy owes me money for working on his jeep
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What else could they be?? :confused:
 
Randy92782 said:
What else could they be?? :confused:
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I dont know. The guy at the shop thinks that they were sleeved and a shop used a smaller diameter valve they had laying around. They dont even sit right in the head. Confused this guy. Some are too big and some are too small.
 
There are 4 different size intake valve head diameters used in SBC heads, 1.72", 1.84", 1.94", and 2.02" and 2 different size exhaust head diameters used 1.5" and 1.6". Not sure if you're talking about head diameter or valve stem diameter but some shops have a machine to grind the valve stem down to a smaller diameter and then they install a bronze sleeve in the guide of which both are fix's for a loose valve guide. The shops that usually do that kind of work are the mass production engine shops that try to save every part they can which means saving money on their end which means more profit.
 
4X4HIGH said:
There are 4 different size intake valve head diameters used in SBC heads, 1.72", 1.84", 1.94", and 2.02" and 2 different size exhaust head diameters used 1.5" and 1.6". Not sure if you're talking about head diameter or valve stem diameter but some shops have a machine to grind the valve stem down to a smaller diameter and then they install a bronze sleeve in the guide of which both are fix's for a loose valve guide. The shops that usually do that kind of work are the mass production engine shops that try to save every part they can which means saving money on their end which means more profit.
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They did that on the stem diameter but 1.37"???? Exhaust that is. 1.72 intake. All the same
 
build the 454 and like said if crank needs any major work ditch it and get a scat 4.250 stroker crank and make 496 out of it.

then if you want more milage and better all around use convert to tbi injection. but if so keep this in mind when building the motor so correct cam and compression specs can be achived.

and for now to try somthing on the cheep swap the axles or gears for somthing other than 3.08 gears. we arnt in the 80s anymore. min of 4.10 would be my choice.

and just cause someone said thay built the motor dosnt mean its built. for all we know its got a cam way off power needs range and mix matched heads with diffrent valve flow specs per head. and possibly a bad compression going on in the worn out motor. then degreased and fresh coat of paint to look like all remaned.
 
Ive heard said once " If he (the seller) says its a 383 stroker, its a 305. If he says its a 400, its a 350" I have actually seen this happen, but not always accurate. The guy can say its a built 350 all day and that doesnt mean squat. It could have come from the junkyard with 250k miles, gotten new rings and bearings, and is now "built"
 
For the $, build the 454. Displacement makes a big difference in building low end torque assuming the cam and intake are matched to the intended RPM. BTW, I run a 396 and have more power than I can use, so it's all relative.
 
I have an 85 SB on 39.5 tires and a mildly built 454, 400 tranny and 4:56 gears, 7 miles to the gallon, 70-75 miles and hour and the air on.
I was thinking about do an nv4500 5spd , maybe I could get 10 mpg !

396 -454 I have ran both , loved both, a 350 in a big truck , just doesnt work for me, it has to work to hard to pull it down the road,, in a trail buggy a 350, geared right, it will work great, 454 in a trail buggy , is a lot of wasted power. just my 2 cents
 
jwglover said:
I have an 85 SB on 39.5 tires and a mildly built 454, 400 tranny and 4:56 gears, 7 miles to the gallon, 70-75 miles and hour and the air on.
I was thinking about do an nv4500 5spd , maybe I could get 10 mpg !

396 -454 I have ran both , loved both, a 350 in a big truck , just doesnt work for me, it has to work to hard to pull it down the road,, in a trail buggy a 350, geared right, it will work great, 454 in a trail buggy , is a lot of wasted power. just my 2 cents
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thanks. drove the truck to work today (about 55miles round trip) and realized that good power and about 11 MPG after working the engine this weekend and changing all fluids throughout. will keep the 350 until I get the gears. Then I will see
 
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